This invention relates to obstruction detection in flow ducts and in particular to a method for detecting an obstruction in an exhaust manifold.
Conventional exhaust manifolds used in automobile manufacturing, for example, are cast using known sand casting methods. As a result, many exhaust manifolds that are produced are blocked or partially blocked by entrapped metal or other material such as sand. Thus, each exhaust manifold is tested for blockage or partial blockage that results from the production process.
One known method of testing for an obstruction includes the use of a ball bearing. The ball bearing is dropped in one end of a port of the manifold and falls by gravity through the manifold and out the opposite end of the port. Each port of the manifold is tested successively. This method suffers from many disadvantages. For example, dropping a ball bearing through each port is time consuming by manufacturing standards. Also, a partial blockage may not be detected depending on the size of the ball bearing and the location of the blockage.
Exhaust manifolds are also tested by connecting a blower to one end of a port, capping all other ports except the port that is being tested for blockage, and measuring back pressure near the blower. An obstruction is detected by comparing the back pressure to a reference value determined from similar, but unobstructed ports. Each port of the manifold is tested successively using this method. While this testing method has achieved extensive use, it suffers from the disadvantage that small obstructions are often undetected because they cause indiscernible changes in the back pressure.
Accordingly, it is an object of an aspect of the present invention to provide a method and apparatus for detection of blockage or partial blockage of an exhaust manifold that mitigates at least some of the disadvantages of the prior art.
In an aspect of the present invention, there is provided a method for detecting an obstruction in a flow duct. The method includes the steps of directing gas through at least one port of the flow duct, measuring a flow noise level of the gas directed through the at least one port, and comparing the noise level with a predetermined noise level. In the event that the flow noise level exceeds the predetermined noise level by at least a threshold amount, then the method includes the step of indicating the presence of an obstruction in the at least one port.
In another aspect of the present invention, the flow duct is an exhaust manifold.
Advantageously, the present invention provides a fast and reliable method of detecting an obstruction in a flow duct, and in particular in an exhaust manifold. The present invention can be integrated into current automotive manufacturing production lines and can be fully automated.